Alito can't vote on any cases where he wasn't there for the arguments and O'Conner's vote doesn't count if the vote is handed down after she has left even if she has heard the arguments. There can never be 10 judges on the supreme court. You need 6 judges for a quorum and the most judges there can be are 9.
Is that written anywhere?
The Constitution provides that there shall be a Supreme Court but leaves it to Congress to determine its size by statute. We started out with six justices, we have had as many as ten, and since 1869 we have had nine. There is no constitutional reason why we should not have fifteen or twenty-five. If Congress allowed it, the number could be anything.
Even if Congress did not allow and increase, the President might choose not to nominate any replacement if one or more judges kicked the bucket leaving the court tilted in his favor. In 1870 the Supreme Court declared the Legal Tender Act invalid by a vote of four to three. There were two vacancies on the Court at the time. President Grant filled these places with two men who promptly voted with the minority of three to reverse the decision by a vote of five to four.
Hmmm... I never tought about that, but I do believe you are correct... It looks like there will necessarily be many 4-4 decisions. GOP has to make this point when arguing for a fast hearing.